Process for manufacture of a zeolite based catalyst for the conversion of methanol to olefins

ABSTRACT

The present invention relates to a process for preparing phosphorus containing zeolite type catalysts based on crystalline aluminosilicates, the catalysts of this process and the use of these catalysts for the conversion of methanol to olefins.

The present invention relates to a process for converting methanol toolefins using catalysts based on crystalline aluminosilicates.

BACKGROUND OF THE INVENTION

Zeolites have been widely studied for the conversion of methanol tohydrocarbons. Among them, ZSM-5 zeolite was the first zeolite studied asactive catalyst for the conversion of oxygenates to hydrocarbons (D.Chang and A. J. Silvestri, Journal of Catalysis 47, 249-259 (1977)).

European patent application EP-A-0 448 000 relates to a process for theproduction of lower olefins from methanol by reacting a mixturecontaining methanol and/or dimethylether on crystalline aluminosilicatesof the pentasil type having a Si/Al atomic ratio of at least 10. Theonly specifically disclosed catalyst is of the pentasil type and has aSi/Al atomic ratio of 103, a sodium content of about 340 ppm, a BETsurface area of 342 m²/g and a pore volume of 0.33 cm³/g. This catalystyields an olefin mixture of more than 6 wt.-% of ethylene, more than 40wt.-% of propylene and less than 30 wt.-% of butenes from a methanoldimethylether mixture.

In the methanol to olefin conversion process deactivation of thecatalyst by coke deposition has been a major drawback. The beneficialeffect of decreasing the crystal size of the pentasil zeolites was shownEP-A-1 424 128 with higher selectivities to propylene and longerlifetime of the catalyst. Nonetheless the initial activity of thecatalyst still is not fully recovered after regeneration when coke hasbeen removed.

U.S. Pat. No. 3,911,041 discloses a catalyst comprising a crystallinealuminosilicate zeolite having a silica to alumina ratio of at leastabout 12 and a constraint index of about 1 to 12. The catalyst containsphosphorus incorporated with the crystal structure in an amount of about3.5 to 4.8 wt.-%. The catalysts are used for the conversion of methanoland dimethylether to an olefin-containing reaction product. The methanolto olefin conversion is less than 2 wt.-%.

U.S. Pat. No. 5,573,990 discloses the conversion of methanol ordimethylether to light olefins by contacting methanol or dimethyletherat a temperature of at least 400° C. with a zeolite ZSM-5 catalystcontaining at least 0.7 wt.-% of phosphorus P and at least 0.97 wt.-% ofrare earth element incorporated within the structure of the catalyst.The ZSM-5 based catalyst is prepared by: mixing a zeolite ZSM-5 catalystwith silica sol and an ammonium nitrate solution, kneading, moulding andcalcining the mixture, ion exchanging with phosphoric acid under reducedpressure, drying and calcining the phosphorus modified zeolite,impregnating the phosphorus modified zeolite with a solution of rareearth elements under reduced pressure, drying and calcining the zeolite,and hydrothermally treating the obtained zeolite at 500-600° C. withwater vapour.

U.S. Pat. No. 4,629,717 concerns a phosphorus modified alumina compositecomprising a hydrogel having a molar ratio on an elemental basis ofphosphorus to aluminum of 1:1 to 1:100 and a surface area of 140 to 450m²/g. The composites are prepared by combining a phosphorus containingcompound and an alumina hydrosol and gelling this mixture. Thiscomposite is used as a catalyst support in the hydrogenation of olefins.

U.S. Pat. No. 6,797,851 and U.S. Pat. No. 7,230,151 relate to a processof making olefins, particularly ethylene and propylene, from anoxygenate feed by use of two or more zeolite catalysts. The firstcatalyst may be a ZSM-5, the second catalyst contains a 10-ringmolecular sieve, and is for example ZSM-22, ZSM-23, ZSM35 or ZSM-48. Theamount of phosphorus, as measured on an elemental basis, is from 0.05 to20 wt.-% based on the weight of the zeolite molecular sieve. The ZSM-5catalyst may be unmodified, phosphorus modified or steam modified,however no specific catalysts or preparation methods thereof aredisclosed.

U.S. Pat. No. 7,368,410 relates to a method for preparing zeolitecatalysts comprising: treating a zeolite with a phosphorus compound toform a phosphorus-treated zeolite; heating the phosphorus-treatedzeolite to a temperature of about 300° C. or higher; combining thephosphorus-treated zeolite with an inorganic oxide binder material toform a zeolite-binder mixture; and heating the zeolite-binder mixture attemperature of about 400° C. or higher to form a bound zeolite catalyst.The catalysts are used for the alkylation of aromatic compounds,especially for the methylation of toluene.

In EP-A-2 025 402 a phosphorus modified molecular sieve and its use inconversion of organics to olefins is disclosed. The molecular sieve maybe prepared by: steaming a zeolite with a Si/Al ratio of below 30 at atemperature ranging from 550 to 680° C.; leaching with an aqueousphosphoric acid solution to remove a part of Al from the zeolite;separation of the zeolite from the liquid; optionally washing thezeolite; and calcining the zeolite.

The existing catalysts have the drawback of limited hydrothermalstability in the process for converting methanol into olefins. Afterextensive studies the present inventors were able to show that anadvantageous stability can surprisingly be achieved by additionallyimpregnating a phosphorus containing zeolite catalyst with low amountsof phosphorus. These catalysts show an unexpected increase in themethanol to olefin (propylene) conversion process especially at lowphosphorus content.

SUMMARY OF THE INVENTION

The present invention concerns a process for manufacturing a zeolitebased catalyst comprising the following steps:

-   -   (a) adding a first phosphorus compound to a zeolite powder of        pentasil type to obtain a phosphorus modified zeolite,    -   (b) adding an aluminum oxide and an acid to the phosphorus        modified zeolite of step (a), and optionally kneading and        homogenizing this mixture,    -   (c) forming, drying and calcining the mixture obtained in        step (b) to obtain formed material, and    -   (d) impregnating the formed material of step (c) with a second        phosphorus compound to obtain a phosphorus modified catalyst.

This invention further relates to the catalysts which are obtained bythe above process, wherein the amount of phosphorus in the catalyst isin the range of from 0.05 and 20 wt.-%, preferably in the range of from0.5 and 10.0 wt.-%, more preferably in the range of from 1.0 to 5.0wt.-%, most preferably in the range of from 1.0 to 3.0 wt.-%, on basisof the total weight of the catalyst.

This invention also relates to the use of this catalyst for convertingmethanol to olefins, especially for converting methanol to propylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the conversion rate of the reference (Δ), inventive () andcomparative (∘) catalysts after hydrothermal treatment in relation tothe amount of phosphorus present in the catalysts.

FIG. 2 shows the second order kinetic rate constant of the reference(Δ), inventive () and comparative (∘) catalysts after hydrothermaltreatment in relation to the amount of phosphorus present in thecatalysts.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a process for preparing a catalyst, basedon crystalline aluminosilicate, with high hydrothermal stability.

The inventive process for manufacturing a zeolite based catalystcomprises the following steps:

-   -   (a) adding a first phosphorus compound to a zeolite powder of        pentasil type to obtain a phosphorus modified zeolite,    -   (b) adding an aluminum oxide and an acid to the phosphorus        modified zeolite of step (a), and optionally kneading and        homogenizing this mixture,    -   (c) forming, drying and calcining the mixture obtained in        step (b) to obtain formed material, and    -   (d) impregnating the formed material of step (c) with a second        phosphorus compound to obtain a phosphorus modified catalyst.

In this process the ratio of the phosphorus of the first phosphoruscompound to the zeolite powder preferably is in the range of 0.05 to 5.0(wt./wt.), more preferably in the range of 0.1 to 2.0 (wt./wt.).

Preferably the zeolite powder used in the inventive process has a Si/Alatomic ratio of about 50 to about 250, more preferably of 50 to 250,even more preferably of about 50 to about 150, still more preferably of50 to 150, and most preferably of 75 to 120.

It is further preferred that in the inventive process the phosphorusmodified zeolite obtained in step (a) is dried at a temperature of from20 to 150° C., more preferably of from 80 to 130° C., most preferably atabout 100° C., and is calcined at a temperature of from 160° C. to 800°C., preferably at a temperature of from 200° C. to 600° C., before thephosphorus modified zeolite is subjected to step (b).

The aluminum oxide is added in step (b) to the phosphorus modifiedzeolite of step (a) in such an amount that the amount of aluminum oxidein the final catalyst is preferably 10 to 80 wt.-%, more preferably 10and 40 wt.-% on basis of the total weight of the catalyst. Preferably,the aluminum oxide is added to the phosphorus modified zeolite of step(a) without prior washing of the phosphorus modified zeolite.

Kneading as described in step (b) of this invention is usually carriedout by using commercial available mixers, e.g. mixer with rotatingmixing tool and fixed mixing chamber, mixer with rotating mixing tooland rotating mixing chamber.

Homogenizing as described in step (b) of this invention is usuallycarried out by using commercial available mixers, e.g. mixer withrotating mixing tool and fixed mixing chamber, mixer with rotatingmixing tool and rotating mixing chamber. Prior to homogenizing, alubricating agent such as, for example, steatite oil, may be added tothe catalyst.

The order of addition of the individual components in step (b) may bevaried. For example, the aluminium oxide can be first blended with anaqueous acid and subsequently mixed with the phosphorus modified zeoliteobtained from step (a). Alternatively, the solid compounds are mixed ina dry state and then combined with an aqueous acid.

The forming process of step (c) may be any process known in the art forforming a catalytic mass into a desired shape. An exemplary formingprocess is extrusion of an extrudable mass with a commercial extrudersuch as, for example, a single-screw extruder or double-screw extruder,to obtain extrudates. Said extrudates may optionally be granulated orpelletized. Other possible shapes are spherical or honeycomb structures.In a particularly preferred embodiment the mixture obtained in step (b)is formed into a desired shape, for example, by one of theabove-mentioned processes, and is subsequently calcined for achievingthe desired stability.

In the process of this invention it is essential that step (c), i.e.,forming, drying and calcining the mixture obtained in step (b), iscarried out before impregnating the zeolite with a second phosphoruscompound in step (d). However, the process does not necessarily excludefurther steps between steps (c) and (d), although it is preferred thatstep (d) is carried out after step (c) without any further steps inbetween.

The first phosphorus compound and the second phosphorus compound may beemployed as a solid or in solution, preferably in an aqueous solution.It is preferred that the first and/or second phosphorus compound is/areemployed in solution. It is further preferred that both the first andthe second phosphorus compound are employed in solution. If the firstphosphorus compound is added to the zeolite powder in a solution, theobtained mixture is usually dried and calcined before being mixed withthe aluminum oxide in step (b).

When the (first and/or second) phosphorus compound is employed inaqueous solution the temperature of the solution is chosen such as tofavor the contact between the aluminum oxide and the phosphoruscompound. When the (first and/or second) phosphorus compound is employedwithout the addition of water or any other (organic or inorganic)solvent the mixture can be submitted to a milling step to favor theintimate contact between the phosphorus compound and catalystcomposition.

In the process of this invention, and in particular in step (c), dryingis usually carried out for 5 min to 24 h, preferably for 1 h to 10 h. Inthe process of this invention, and in particular in step (c), calciningis usually carried out for 10 min to 10 h, preferably for 30 min to 6 h.

In the process of this invention, and in particular in step (c), dryingis usually carried out at a temperature of from 20 to 150° C., morepreferably of from 80 to 130° C., most preferably at about 100° C. Inthe process of this invention, and in particular in step (c), calciningis usually carried out at a temperature of from 160° C. to 800° C.,preferably at a temperature of from 200° to 600° C.

Preferably calcination (and in particular calcination in step (c)) iscarried out without treatment with steam (water vapor). In particular,it is preferred that during calcination no steam is fed from the outsidewhile heating the mixture. It is known in the art that steam treatmentof zeolites results in dealumination of the zeolites and in an increaseof the Si/Al atomic ratio. In the present invention, dealumination andtransformation of the zeolite by steam is undesirable, and it ispreferred that both the zeolite framework is left untransformed and theSi/Al atomic ratio is left unchanged prior to impregnating with a secondphosphorus compound.

It is preferred that the zeolite powder used in the inventive processhas a Si/Al atomic ratio of about 50 to about 250, more preferably ofabout 50 to about 150, and most preferably of 75 to 120.

In the process of the present invention the first and second phosphoruscompound are preferably independently selected from inorganic phosphoruscontaining acids, organic phosphorus containing acids, alkaline, earthalkaline and/or ammonium salts of inorganic phosphorus containing acidsor organic phosphorus containing acids, phosphorus (V) halides,phosphorus (III) halides, phosphorus oxyhalides, phosphorus (V) oxide,phosphorus (III) oxide, and mixtures thereof.

It is further preferred in the process of the present invention that thefirst and second phosphorus compound are independently selected fromPY₅, PY₃, POY₃, M_(x)E_(z)/₂H_(3-(x+z))PO₄, M_(x)E_(z)/₂H_(3-(x+z))PO₃,P₂O₅, and P₄O₆, wherein:

Y represents F, Cl, Br or I, preferably Cl,

x=0, 1, 2, or 3,

z=0, 1, 2, or 3,

wherein x+z≦3,

M independently represents an alkaline metal and/or ammonium, and

E represents an earth alkaline metal.

It is even more preferred that the first and second phosphorus compoundemployed in the process of the present invention are independentlyselected from H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄, and (NH₄)₃PO₄.

In the process of the present invention it is most preferred that thefirst phosphorus compound is H₃PO₄ and the second phosphorus compound is(NH₄)H₂PO₄.

In the process of the present invention the aluminum oxide used in step(b) is preferably aluminum oxide or aluminum oxide hydrate, mostpreferably aluminum oxide hydrate.

The acid used in step (b) of the process of the present invention isusually an inorganic or organic acid, preferably sulfuric acid, nitricacid, acetic acid, formic acid, oxalic acid or citric acid, morepreferably nitric acid, acetic acid or citric acid, and most preferablynitric acid. It is further preferred that in step (b) the acid isapplied in aqueous solution.

In a preferred embodiment the overall amount of phosphorus added in theinventive process is in the range of from 0.05 and 20 wt.-%, preferablyin the range of from 0.5 and 10.0 wt.-%, more preferably in the range offrom 0.5 and 5.0 wt.-%, most preferably in the range of from 1.0 to 3.0wt.-% on basis of the total weight of the phosphorus modified catalyst.

In a further especially preferred embodiment the present inventionprovides a catalyst which can be obtained by the inventive process. Theamount of phosphorus in this catalyst is usually in the range of from0.05 and 20 wt.-%, preferably in the range of from 0.5 and 10.0 wt.-%,more preferably in the range of from 1.0 to 5.0 wt.-%, most preferablyin the range of from 1.0 to 3.0 wt.-%, on basis of the total weight ofthe catalyst.

In a further preferred embodiment the catalyst of this invention has aSi/Al atomic ratio in the range of from 50 to 250, preferably of from 50to 150, most preferably of from 75 to 120.

In another preferred embodiment, the catalyst of this invention has anAl:P atomic ratio of 2.4 or more, preferably in the range of 2.4 to14.1, more preferably in the range of 4.5 to 6.0, and even morepreferably in the range of 4.6 to 5.9. It is most preferably that thecatalyst of this invention has an Al:P atomic ratio of about 5.9.

The zeolite employed in step (a) of the process of the present inventionis a zeolite of the pentasil type. The zeolite can possess a structureas described in “Atlas of Zeolite Framework Types” (Ch. Baerlocher, W.M. Meier, D. H. Olson, Elsevier, Fifth Revised Edition, 2001), thedisclosure of which in this connection is incorporated into thisapplication by way of reference. Preferred zeolites of the presentinvention are zeolites having MFI or MEL structure. A preferred zeoliteof the MFI structure is ZSM-5. A preferred zeolite of the MEL structureis ZSM-11. The zeolites employed in step (a) of the process of thepresent invention are preferably of the H-type, i.e., are protonatedzeolites. Most preferably, the zeolite used in the present invention isH-type ZSM-5.

The zeolite employed in the process of the present invention has a poresize in the range of preferably 4.0 Å to 6.0 Å, more preferably in therange of 4.8 Å to 5.8 Å.

The zeolite powder of step (a) is preferably obtained by adding atemplate to the synthesis gel composition. Preferred templates aretetraalkylammonium hydroxide such as tetrapropylammonium hydroxide(TPAOH), or tetrapropylammonium bromide (TPABr). Other templates thatmay be used in the preparation of the zeolite powder of step (a) aremixtures of ammonia or an organic amine compound with a further organiccompound selected from the group of alcohols, preferably butyl alcohol.

The catalyst obtainable by the process of the present inventionpreferably has a pore volume,measured by means of mercury porosimetryaccording to DIN 66133, of 0.25 to 0.8 cm³/g, more preferably of 0.28 to0.40 cm³/g

In a preferred embodiment of this invention the phosphorus modifiedcatalyst obtained in step (d) is subjected to a further drying step. Inanother preferred embodiment of this invention the phosphorus modifiedcatalyst obtained in step (d) is subjected to a further calcinationstep.

The catalyst described in this invention is useful in a process for theconversion of methanol to olefins, especially propylene.

The catalyst described in this invention is preferably useful in aprocess for the conversion of methanol to olefins, especially propylene,when the zeolite powder used in the inventive process has an Si/Alatomic ratio of about 50 to about 250, more preferably of 50 to 250,even more preferably of about 50 to about 150, still more preferably of50 to 150, and most preferably of 75 to 120.

Hydrothermal stability of the catalysts can established by measuring theactivity in the reaction of methanol to olefins, especially propylene,after calcination of the catalyst at temperatures from 700 to 750° C. inan atmosphere of 100% steam for a period of time of from 3 to 8 h. Thistreatment emulates in short time the long-term behavior of amethanol-to-propylene catalyst after many cycles ofreaction-regeneration in which water is always present. It has beenshown that the calcination in the presence of steam in the absence ofphosphorus causes the dealumination of the zeolitic framework, resultingin the loss of the Brönsted acidity and consequently decreasing theactivity and life time of the catalyst. With the addition of phosphorusdistributed in both zeolite and alumina binder, as claimed in thepresent invention, the activity of the catalyst is preserved.

EXAMPLES Reference Example 1

61 kg of deionized water and 57 kg of a commercially available,peptizable aluminum oxide hydrate (Pural SB®, Sasol) having a particlesize distribution of 91% by volume≦90 μm; 51% by volume≦45 μm, and 27%by volume≦25 μm were blended in a commercial kneader. A solution of 39kg 57.2% nitric acid and 30 kg deionized water were slowly added. Theresulting solution was kneaded for 60 minutes until plasticization andhomogenization had occurred. Subsequently 235 kg of calcined H-zeolitepowder with a silicon-to-aluminum atomic ratio of 105 and an averageparticle diameter of the primary crystals of 0.03 μm, which had beenground to a particle size of less than about 500 μm by means of acommercial mill, were added. Mixing was continued for another 30minutes, and about 25 kg of additional water was added to improve theconsistency of the compound. After blending in 20 kg of steatite oil andmixing for another 10 minutes, the plasticized compound was extruded ina commercial extruder into shaped articles having a diameter of about 3mm and a length of about 5 mm. The shaped articles were then dried for16 hours at 120° C. and subsequently calcined for 5 hours at 600° C.

This sample is hereinafter identified as Reference Example 1. Thechemical composition of the catalyst is shown in Table 1.

Example 1

1200 g of calcined H-zeolite powder with a silicon-to-aluminum atomicratio of 105 and an average particle diameter of the primary crystals of0.03 μm, which had been ground to a particle size of less than about 500μm by means of a commercial mill, was suspended in 6012 g of an aqueoussolution containing 12 g orthophosphoric acid (85 wt.-%) and refluxedfor 2 h. After drying at 100 to 110° C. and calcining at 540° C. for 10h, a phosphorus modified zeolite was obtained.

700 g of this phosphorus modified zeolite was dry mixed in acommercially available double-Z-Kneader together with 178 g commerciallyavailable, peptizable aluminum oxide hydrate (Pural SB®, Sasol) with aparticle size distribution of 91 Vol.-%≦90 μm; 51 Vol.-%≦45 μm and 27Vol.-%≦25 μm, and 28 g paraffin wax.

245 g demineralized water, 49 g of a 5 wt.-% nitric acid solution andthen further 109 g demineralized water were slowly added to this mixtureunder kneading.

After addition of 56 g steatite oil the mixture was homogenized. Thehomogenized mixture was then blown with air until an extrudable mass wasobtained. The mass was extruded with a commercially availablesingle-screw extruder to extrudates with a diameter of approximately 3mm and a length of approximately 6 mm. These extrudates were dried at120° C. for 16 h and then calcined at 550° C. for 5 h. The extrudateshave a P content of 0.2 wt.-% on basis of the total weight of thecatalyst. The overall chemical composition is 82.9 wt.-% SiO₂, 16.7wt.-% Al₂O₃ and 0.5 wt.-% P₂O₅.

A 100 ml spherical flask is charged with 10 ml redistilled water and0.019 g ammonium dihydrogen phosphate (99 wt.-%) under stirring. To thissolution 1 g of the phosphorus containing extrudates, ground to agranulate with a particle size in the range of 0.2 to 0.4 mm, are added.The suspension is slowly evaporated (1 hour) in a rotary vacuumevaporator at 80° C. until dryness. The solid product is further driedat 100° C. for 2 h and calcined at 650° C. for 3 h. The obtainedcatalyst has a P content of 0.7 wt.-% on basis of the total weight ofthe catalyst. The chemical composition of the catalyst of example 1 isshown in Table 1.

Examples 2 to 4

The catalysts of examples 2 to 4 were obtained analogously to example 1by using 0.056 g, 0.075 g and 0.15 g ammonium dihydrogen phosphate,respectively. They have a P content of 1.7 wt.-%, 2.2 wt.-% and 4.2wt.-%, on basis of the total weight of the catalyst. The chemicalcompositions of the inventive catalysts of examples 2 to 4 are shown inTable 1.

TABLE 1 Chemical composition and Al:P ratio of the catalysts ofReference Example 1 and Examples 1 to 4 Ref.- Example Example ExampleExample Catalyst Example 1 1 2 3 4 P wt.-% 0 0.7 1.7 2.2 4.2 SiO₂ wt.-%82.6 81.9 80.1 79.0 75.9 Al₂O₃ wt.-% 17.4 16.5 16.1 16.0 15.3 P₂O₅ wt.-%0 1.6 3.8 5.0 8.8 Al:P (mol/mol) — 14.1 5.9 4.6 2.4

As comparative examples the aluminum oxide was modified with aphosphorus compound and then combined with the zeolite.

Comparative Example 1

175 g demineralized water and 175 g commercially available, peptizablealuminum oxide hydrate (Pural SB®, Sasol) with a particle sizedistribution from 91 Vol.-%≦90 μm; 51 Vol.-%≦45 μm and 27 Vol.-%≦25 μmwere mixed in a commercially available double-Z-Kneader. 214 g of a 30wt.-% nitric acid solution were slowly added to this mixture andhomogenized until plastification occurred.

16 g orthophosphoric acid (85 wt.-%) and subsequently 700 g calcinedH-zeolite powder with a silicon-to-aluminum atomic ratio of 105 and anaverage particle diameter of the primary crystals of 0.03 μm, which hadbeen ground to a particle size of less than about 500 μm by means of acommercial mill, were slowly added and the mixture kneaded. Afteraddition of 10 g steatite oil and 14 g demineralized water the mixturewas homogenized. The homogenized mixture was then blown with air untilan extrudable mass was obtained. The mass was extruded with acommercially available single-screw extruder to extrudates with adiameter of approximately 3 mm and a length of approximately 6 mm. Theseextrudates were dried at 120° C. for 16 h and then calcined at 550° C.for 5 h.

The obtained extrudate is hereinafter identified as Comparative Example1 and has a P content of 0.5 wt.-% on basis of the total weight of thecatalyst. The chemical composition is shown in Table 2.

Comparative Examples 2 to 4

The catalysts of comparative examples 2, 3 and 4 were obtainedanalogously to comparative example 1 by using 64 g, 127 g respectively190 g orthophosphoric acid (85 wt.-%). The obtained catalysts have a Pcontent of 2.0, 3.8 and 5.5 wt.-% on basis of the total weight of thecatalyst. The chemical compositions of comparative catalysts 2 to 4 areshown in Table 2.

TABLE 2 Chemical composition and Al:P ratio of the catalysts ofComparative Examples 1 to 4. Comp.- Comp.- Comp.- Comp.- CatalystExample 1 Example 2 Example 3 Example 4 P wt.-% 0.5 2.0 3.8 5.5 SiO₂wt.-% 82.8 79.7 76.1 72.7 Al₂O₃ wt.-% 16.1 15.6 14.9 14.3 P₂O₅ wt.-% 1.14.7 9.0 13.0 Al:P (mol/mol) 20.0 4.6 2.3 1.5

Application Examples

The hydrothermal stability of the catalysts was measured by performingthe reaction of methanol to propylene in the presence of the catalystswhich had previously been subjected to a hydrothermal treatment. Thehydrothermal treatment was carried out as follows: The catalysts werepelletized to a particle size in the range of 0.2 to 0.4 mm and placedin small crucibles in an oven. Then they were subjected to a temperatureof about 700° C. for about 5 h, with continuous feeding of water at 1.5ml/min.

The hydrothermally treated samples were tested in an isothermal fixedbed reactor for the conversion of methanol to propylene. The reactionconditions used were:

-   -   methanol/water=1:2 wt./wt.    -   weight hourly space velocity        -   WHSV(MeOH)=1 h⁻¹, WHSV(H₂O)=2 h⁻¹    -   outlet pressure=1.02 bar    -   reaction temperature=450° C.    -   amount of catalyst=0.5 g    -   particle size: 0.2 to 0.4 mm.

The methanol-water mixture was fed by means of a KDS dual syringe pump.0.5 g catalyst was placed in a glass reactor of 15 mm diameter and thetemperature was controlled by means of a k-thermocouple inserted insidethe bed. Above the catalyst bed a bed of quartz sand was placed toensure a good vaporization of the feed.

The outlet of the reactor was thermostatized at 150° C. and the productswere automatically analyzed each 30 min in two Gas Chromatographs HP5890with FID detectors. First, with a capillary column HP-PONA 50 m 0.25 mmID, that allows the separation of methane, ethane+ethylene,propane+propylene, dimethylether, methanol+isobutane, n-butane, butenes,and C5+ (higher hydrocarbons), with a temperature program starting at30° C. up to 250° C. Second, in a Plot-Alumina column with dimensions of30 m and 0.53 mm, for the separation of ethane, ethylene, propane,propylene and isobutane, with a temperature program from 50° C. to 190°C.

Conversion is defined as the sum of the yields of products differentfrom methanol and dimethylether relative to the sum of the yields of allproducts of educts. Selectivity is defined as yield of a specificproduct divided by sum of the yields of all products.

The kinetic rate of a catalyst is an indication of its activity. It maybe described by its second order kinetic rate constant which can be usedfor comparison of catalysts tested at the same spatial velocity. Therate constant may be calculated as follows:

${{rate}\mspace{14mu} {constant}} = {\frac{conversion}{{100\mspace{14mu} {{wt}.\mspace{14mu} \%}} - {conversion}}.}$

The catalysts from Reference Example 1, Examples 1 to 4 and ComparativeExamples 1 to 4 were tested after hydrothermal treatment at 700° C. for5 h in the reaction of methanol to propylene. The conversion percentageand kinetic rate constants are shown in Table 3. The conversion and thekinetic rate are additionally displayed in FIGS. 1 and 2.

TABLE 3 Conversion and kinetic rate of catalysts of reference example 1,inventive examples 1 to 4 and comparative examples 1 to 4 afterhydrothermal treatment at 700° C. for 5 hours. Catalyst Conversion[wt.-%] Kinetic rate constant Ref.-Ex. 1 68.7 2.2 Ex. 1 90.6 9.6 Ex. 297 32.3 Ex. 3 96.1 24.3 Ex. 4 90.5 9.5 Comp.-Ex. 1 77.5 3.4 Comp.-Ex. 283.9 5.2 Comp.-Ex. 3 81.3 4.3 Comp.-Ex. 4 79.7 3.9

It can be clearly seen that the catalysts of inventive examples 1 to 4which have been additionally impregnated with a phosphorus compoundyield higher conversions than the comparative catalysts where thephosphorus is only bound within the zeolite. Moreover, when activity ismeasured in terms of second order kinetic rate constant, the activity ofthe inventive catalysts is up to six times higher than of thecomparative catalysts.

1. A process for manufacturing a zeolite based catalyst comprising thefollowing steps: (a) adding a first phosphorus compound to a zeolitepowder of pentasil type to obtain a phosphorus modified zeolite, (b)adding an aluminum oxide and an acid to the phosphorus modified zeoliteof step (a), (c) forming, drying and calcining the mixture obtained instep (b) to produce a formed material, and (d) impregnating the formedmaterial of step (c) with a second phosphorus compound to obtain aphosphorus modified catalyst.
 2. The process according to claim 1,wherein the ratio of the phosphorus of the first phosphorus compound tothe zeolite powder is in the range of 0.05 to 5.0 (wt./wt.).
 3. Theprocess according to claim 1, wherein the modified zeolite of step (a)is dried at a temperature from 20 to 150° C., and is calcined at atemperature of from 160° C. to 800° C., before being subjected to step(b).
 4. The process according to claim 1, wherein the first and secondphosphorus compounds are selected from the group consisting of inorganicphosphorus containing acids, organic phosphorus containing acids,alkaline, earth alkaline and ammonium salts of inorganic phosphoruscontaining acids and organic phosphorus containing acids, phosphorus (V)halides, phosphorus (III) halides, phosphorus oxyhalides, phosphorus (V)oxide, phosphorus (III) oxide, and mixtures thereof.
 5. The processaccording to claim 1, wherein the first and second phosphorus compoundsare selected from the group consisting of PY₅, PY₃, POY₃,M_(x)E_(z)/₂H₃-(x+z)PO₄, M_(x)E_(z)/₂H₃-(x+z)PO₃, P₂O₅, and P₄O₆,wherein: Y represents F, Cl, Br or I, x=0, 1, 2, or 3, z=0, 1, 2, or 3,wherein x+z≦3, M represents an alkaline metal and/or ammonium, and Erepresents an earth alkaline metal.
 6. The process according to claim 5,wherein the first and second phosphorus compounds are selected from thegroup consisting of H₃PO₄, (NH₄)H₂PO₄, (NH₄)₂HPO₄ and (NH₄)₃PO₄.
 7. Theprocess according to claim 1, wherein the first phosphorus compoundcomprises H₃PO₄ and the second phosphorus compound comprises (NH₄)H₂PO₄.8. The process according to claim 1, wherein the aluminum oxide used instep (b) is comprises aluminum oxide hydrate.
 9. The process accordingto claim 1, wherein the amounts of the phosphorus compound added in step(a), of the aluminum oxide added in step (b), and of the phosphoruscompound added in step (d) are chosen such that the Al:P atomic ratio inthe phosphorus modified catalyst obtained in step (d) is 2.4 or more.10. The process according to claim 1, wherein the acid used in step (b)is selected from the group consisting of sulfuric acid, nitric acid,acetic acid and citric acid.
 11. The process according to claim 1,wherein the zeolite powder of step (a) has a Si/Al atomic ratio of about50 to about
 250. 12. A catalyst obtainable by the process according toclaim 1, wherein the amount of phosphorus in the catalyst is in therange of from 0.05 and 20 wt.-%.
 13. The catalyst according claim 12,wherein the Si/Al atomic ratio is in the range of from 50 to
 250. 14.The catalyst according claim 12, wherein the Al:P atomic ratio is 2.4 ormore.
 15. (canceled)
 16. The process of claim 9, wherein the Al:P atomicratio is in the range of 2.4 to 14.1.
 17. The catalyst of claim 14,wherein the Al:P atomic ratio is in the range of 2.4 to 14.1.
 18. Theprocess according to claim 1, wherein the zeolite powder of step (a) hasa Si/Al atomic ratio of about 50 to about
 150. 19. The catalystaccording claim 12, wherein the Si/Al atomic ratio is in the range offrom 50 to
 150. 20. Process for converting methanol to olefinscomprising passing methanol over the catalyst of claim 12.